I'll answer what I can....
2. Yes, a wideband is absolutely necessary. You really don't know whats going on fuel/air wise without it. Placement is dependent on your exhaust setup and if you are turbo/NA. The distance between the sensor and either the turbo or exhaust is slightly different..I am not sure if it is significant but too close and you'll burn up the sensor in short order.
3. I think most ppl keep the stock pcm to run gauges. If you eliminate it, you'd need standalone gauges or converters to interpret the signals.
4. Depends on how beat your motor is and how much ya plan on beating on it. A whooped motor probably won't last long boosted. If this is your first foray into motor building and crap, I'd start by getting the motor into good condition first. I'd definitely do all the work yourself.
Good luck!
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